Add admin command tests for setDefaultRWConcern

[vic-tsang]

This PR contains:

• admin command tests for setDefaultRWConcern

Ref:

• Issue Add compatibility test for setDefaultRWConcern #429

[documentdb-triage-tool]

🤖 Auto-triaged by documentdb-triage-tool.

Applied: compatibility test, enhancement
Project fields suggested: Component test-coverage · Priority P2 · Effort L · Status Needs Review
Confidence: 0.30 (deterministic)

Reasoning

component from path globs (test-coverage); effort from diff stats (709+0 LOC, 11 files); LLM failed: Invalid response body while trying to fetch https://api.anthropic.com/v1/messages: Premature close

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[SaiPradyumn]

administration/utils/admin_test_case.py is added again — also added in PRs #642 and #646 (still open). Critically, the schema differs: this PR's version has setup_commands: tuple = (), while #642/#646 have use_admin: bool = True. When these merge, one version will overwrite the other and break tests in one of those PRs.